Showing papers by "Stephanie Hansen published in 2012"

Magnetically Driven Implosions for Inertial Confinement Fusion at Sandia National Laboratories

Abstract: High current pulsed-power generators efficiently store and deliver magnetic energy to z-pinch targets. We review applications of magnetically driven implosions (MDIs) to inertial confinement fusion. Previous research on MDIs of wire-array z-pinches for radiation-driven indirect-drive target designs is summarized. Indirect-drive designs are compared with new targets that are imploded by direct application of magnetic pressure produced by the pulsed-power current pulse. We describe target design elements such as larger absorbed energy, magnetized and pre-heated fuel, and cryogenic fuel layers that may relax fusion requirements. These elements are embodied in the magnetized liner inertial fusion (MagLIF) concept [Slutz “Pulsed-power-driven cylindrical liner implosions of laser pre-heated fuel magnetized with an axial field,” Phys. Plasmas, 17, 056303 (2010), and Stephen A. Slutz and Roger A. Vesey, “High-Gain Magnetized Inertial Fusion,” Phys. Rev. Lett., 108, 025003 (2012)]. MagLIF is in the class of magneto-inertial fusion targets. In MagLIF, the large drive currents produce an azimuthal magnetic field that compresses cylindrical liners containing pre-heated and axially pre-magnetized fusion fuel. Scientific breakeven may be achievable on the Z facility with this concept. Simulations of MagLIF with deuterium-tritium fuel indicate that the fusion energy yield can exceed the energy invested in heating the fuel at a peak drive current of about 27 MA. Scientific breakeven does not require alpha particle self-heating and is therefore not equivalent to ignition. Capabilities to perform these experiments will be developed on Z starting in 2013. These simulations and predictions must be validated against a series of experiments over the next five years. Near-term experiments are planned at drive currents of 16 MA with D2 fuel. MagLIF increases the efficiency of coupling energy (=target absorbed energy/driver stored energy) to targets by 10-150X relative to indirect-drive targets. MagLIF also increases the absolute energy absorbed by the target by 10-50X relative to indirect-drive targets. These increases could lead to higher fusion gains and yields. Single-shot high yields are of great utility to national security missions. Higher efficiency and higher gains may also translate into more compelling (lower cost and complexity) fusion reactor designs. We will discuss the broad goals of the emerging research on the MagLIF concept and identify some of the challenges. We will also summarize advances in pulsed-power technology and pulsed-power driver architectures that double the efficiency of the driver.

Investigation of high-temperature bright plasma X-ray sources produced in 5-MA X-pinch experiments.

Abstract: Using solid, machined $\mathsf{X}$-pinch targets driven by currents rising from 0 to 5--6 MA in 60 ns, we observed bright spots of 5--9-keV continuum radiation from $5\ifmmode\pm\else\textpm\fi{}2\mathrm{\text{\ensuremath{-}}}\ensuremath{\mu}\mathrm{m}$ diameter regions. The $g6\mathrm{\text{\ensuremath{-}}}\mathrm{keV}$ radiation is emitted in about 0.4 ns, and the bright spots are roughly 75 times brighter than the bright spots measured at 1 MA. A total x-ray power of 10 TW peak and yields of $165\ifmmode\pm\else\textpm\fi{}20\text{ }\text{ }\mathrm{kJ}$ were emitted from a 3-mm height. The 3--5-keV continuum radiation had a 50--90-GW peak power and 0.15--0.35-kJ yield. The continuum is plausibly from a $1275\ifmmode\pm\else\textpm\fi{}75\mathrm{\text{\ensuremath{-}}}\mathrm{eV}$ blackbody or alternatively from a $3500\ifmmode\pm\else\textpm\fi{}500\mathrm{\text{\ensuremath{-}}}\mathrm{eV}$ bremsstrahlung source.

Time and space resolved measurement of the electron temperature, mass density and ionization state in the ablation plasma between two exploding Al wiresa)

Abstract: We have determined the properties of plasma around and between two exploding wires using high-resolution x-ray absorption spectroscopy. Plasma densities and temperatures ranging from ≳0.1g/cm3 and a few eV to less than 0.01 g/cm3 and 30 eV have been measured in experiments at Cornell University with two 40 μm aluminum (Al) wires spaced 1 mm apart driven by ∼150 kA peak current pulses with 100 ns rise time. The wire plasma was backlit by the 1.4–1.6 keV continuum radiation produced by a Mo wire X-pinch. The spectrometer employed two spherically bent quartz crystals to record the absorption and backlighter spectra simultaneously. The transition between the dense Al wire core and the coronal plasma is seen as a transition from cold K-edge absorption to Mg-, Na-, and finally Ne-like absorption at the boundary. In the plasma that accumulates between the wires, ionization states up to C-Like Al are observed. The spectrometer geometry and ∼2μm X-pinch source size provide 0.3 eV spectral resolution and 20 μm spat...

Investigating inertial confinement fusion target fuel conditions through x-ray spectroscopya)

Abstract: Inertial confinement fusion (ICF) targets are designed to produce hot, dense fuel in a neutron-producing core that is surrounded by a shell of compressing material. The x-rays emitted from ICF plasmas can be analyzed to reveal details of the temperatures, densities, gradients, velocities, and mix characteristics of ICF targets. Such diagnostics are critical to understand the target performance and to improve the predictive power of simulation codes.

Calibration and analysis of spatially resolved x-ray absorption spectra from a nonuniform plasma

Abstract: We report here the calibration and analysis techniques used to obtain spatially resolved density and temperature measurements of a pair of imploding aluminum wires from x-ray absorption spectra. A step wedge is used to measure backlighter fluence at the film, allowing transmission through the sample to be measured with an accuracy of ±14% or better. A genetic algorithm is used to search the allowed plasma parameter space and fit synthetic spectra with 20 μm spatial resolution to the measured spectra, taking into account that the object plasma nonuniformity must be physically reasonable. The inferred plasma conditions must be allowed to vary along the absorption path in order to obtain a fit to the spectral data. The temperature is estimated to be accurate to within ±25% and the density to within a factor of two. This information is used to construct two-dimensional maps of the density and temperature of the object plasma.

A Renewed Argon Gas Puff Capability on Sandia's Z Machine (UUR version).

Abstract: Summary form only given. We have reestablished gas puff z-pinch capability on Sandia's 20 MA Z machine, including a Sandia-operated driver system and an imaging interferometer to characterize nozzle mass flow [1]. Initial experiments have focused on developing a 3 keV Ar K-shell x-ray source. We have pursued a design-driven approach to planning these experiments, utilizing numerical simulation to predict Ar K-shell yield for various nozzle mass profile configurations. In particular, we study coupling to the generator and how the distribution of mass between the two shells impacts magnetic Rayleigh-Taylor instability evolution. Two-dimensional radiation-magneto-hydrodynamic (MHD) simulations at NRL for a number of density profiles produced by the nozzle have predicted yields in excess of 300 kJ, and indicated that a 1:1.6 outer-to innershell mass ratio would produce the most stable implosion with high enough temperature to optimize Ar K-shell output [2]. This result was also consistent with 3D MHD modeling using the Gorgon code [3] at Sandia. Both models used tabulated non-LTE atomic models for Ar K-shell photon emission. We will present Z experimental data from the first gas puff shots on the accelerator since 2006, and compare these to the numerical models. Spectral output is measured from 1-20 keV. Electrical current measurements at different positions along the power flow section provide information on current coupling to the load. Time-gated pinhole imaging and radially-resolved spectroscopy indicate ~60 cm/μs implosion velocities and >1 keV electron temperatures.